1. Field of the Invention
The present invention relates to a method and an apparatus for controlling a brushless DC motor used in a magnetic disk apparatus and the like.
2. Description of the Related Art
In a conventional magnetic disk apparatus, a brushless DC (direct current) motor such as a spindle motor is used to rotate a recording medium (disk), and the brushless DC motor has to be reliably started (driven) in order to use the magnetic disk apparatus. In a conventional brushless DC motor control apparatus, therefore, a value of current supplied to the brushless DC motor is preset in view of various situations, and a drive current corresponding to the current value is supplied to the brushless DC motor when the brushless DC motor is started.
Since the current value is set in view of various situations, the brushless DC motor can reliably be started, irrespective of the situations. In a normal starting operation, however, a drive current to the brushless DC motor overflows.
Battery-driven magnetic disk apparatuses have recently been employed. To save power in these apparatuses, an unnecessary current has to be prevented from flowing to a brushless DC motor. When a magnetic disk apparatus is incorporated into a power-save type computer system, an unnecessary current increases in accordance with an increase in the number of start/stop operations of a brushless DC motor.
It is thus desired to realize a brushless DC motor control apparatus in which a drive current supplied to a brushless DC motor is reduced to reliably start the brushless DC motor.